This invention relates to a process for the production of pulp. More particularly, the invention relates to a process for the production of pulp from lignocellulosic materials by carrying out the cooking in the presence of a small amount of a novel type of cooking aid selected from the group consisting of hydroxyanthracenes and derivatives thereof. The cooking aid can be added to a cooking liquor in any of the conventional alkaline or sulfite or the like cooking processes. The term "alkaline cooking process" or simply "alkaline process" herein used includes various alkaline cooking processes such as a kraft process, a soda process, a sodium carbonate process and the like. Similarly, the term "sulfite cooking process" or simply "sulfite process" herein used includes various sulfite cooking processes such as an alkaline sulfite process, a neutral sulfite process, a bisulfite process, and the like.
In the field of producing pulp from lignocellulosic material such as wood, bagasse, hemp and the like, numerous attempts have been made, repeatedly, from ancient times to improve the cooking yield, the rate of cooking and the quality of the product pulp, aiming at the economical production of good quality pulp with decreased consumption of raw material and of energy. For example, instead of the conventional kraft process in which lignocellulosic material such as wood is subjected to treatment by a cooking liquor comprising essentially sodium hydrate and sodium sulfide, a modified process thereof which is usually called a "polysulfide process" and is characterized by being subjected to treatment with a cooking liquor comprising a sodium polysulfide is currently more popularly employed. Various other modifications, for example, the addition of borohydride, hydrazine, hydroxylamine or the like have also been proposed and tried. Most such modified processes, however, have not been useful in a practical manner because in some cases total or partial change of the processing equipment is required. In other cases, there is a significant increase in production costs. In still other cases, the process is not applicable to soft woods or to hard woods, or both. Thus, except for said polysulfide process, none of the above-mentioned prior art processes is more than a laboratory model.
The object of the present invention is to provide a novel process for the production of pulp free from the disadvantages mentioned above.